DIY Video Projector

[tech head]

I think that the best way to do keystone correction is with a mirror.
flip your lcd around to reverse the image then use a mirror to flip it back. By changing the angle of the mirror you can change the keystone factor.
If the light path from the projector is square with the screen in the reflected image then there will be no keystone effect.

btw
the mirror should be after the optics :-)

[piGuy]

Hi there everyone. You can count me as one of the countless people who's been following this thread and hasn't contributed yet. I noticed there's been some talk of building a reflector. I was wondering if anyone has looked into aluminized mylar for a reflective surface. It's dirt cheap, and the good quality stuff has over 90% reflection. I was interested in building a solar concentrator at one time, and builders use aluminized mylar to produce a mirror-like finish on a parabolic surface. It would take some practice to put on properly, but the end result should work quite well. Also, I'm very interested in mountain_nz's idea. It sounds great. Also hoping not everyone has given up hope on the CRT idea? I think for a really good quality hi-res image, CRT would be just about the only way to go. I found this thread after looking for a way to display the video from my newly purchased HDTV tuner set top box. I plugged it in to an ancient old 14" computer monitor and the picture is absolutely jaw dropping. It makes me want to look into crt-based ideas... The scan rate for 1080i HDTV is ~33.75khZ. That's not a huge leap from mountain_nz's NTSC based ~15khz... (Sorry, I'm nowhere near an expert on display systems). I'm willing to crack open this 14" monitor and start playing around. :-)

[xblocker]

Mountain,
as far as i understand your construction, it is similar to laserprojector concept. But the lighting design can't work! It's unpossible to couple a focused LED light cone into a fibre pipeline and get out a parallel lightbeam. Even if you would focus the sun into it...! Also the light emitting LEDs don't produce parallel light. Most of the LEDs light is wasted and doesn't reach the fibre's aperture. Make a ray traycing and you see it. This is only possible with laser light and momo mode fibre optics, as far as i know.
Look at this:

[piGuy]

Almost forgot, for those interested in LCD projection:
If you want to open up a LCD monitor, a good choice might be the 15" model from Solarism. It has a 25ms response rate, which virtually eliminates blurring from the LCD. It's got S-video and composite inputs as well. Although it's a little pricey (I think around $500). It also has the brightest backlight on the market, even though it wouldn't really be useable in a projection system.

[tech head]

xblocker

It is possible to do it. you can use a focusing lense to bring the image down to the size of the fiber then use a micro pcx lens to make the light ray parallel. then it would have laser like properties.

[SuperDave]

oftheend...thats great to hear about the light.

Is the bulb really large like the MV bulbs? Does it have one of those STUPID "eyes" at the top?

what about light distribution, are you getting any bright spots?

Is your new light setup basically the same as before (i.e. taken from a dusk-to-dawn light) or did you order from elsewhere?

I was looking at my stuff last night (which I havent touched for 2 weeks) and I realized that I have probably been taking the wrong approach with my light. I have been pointing my light at the fresnel. I think a lot of the light gets defracted away from the freslen because of the sharp angles at the tip of the light and the "eye" thing at the tip. I wan to try standing the light up and see if I get better results....It's hard for me to explain and those that havent seen the MV lights probably have no idea what I'm talking about. I am pretty sure oftheend will because I want to try placing my light the way he has his (you can see a picture or link to his about 10 pages back or so...and a picture of mine is attached below.

[SuperDave]

I will be working on a new reflector this weekend. Thanks to some tips from tech_head on creating my mold, I hope I can at least build a fiberglass reflector this weekend (although I know I wont have time by then to get it electroplated).

I will be making an elipsoidal reflector...but I think I would also like to make a parabolic reflector. Here is my reaoning...please tell me if I'm wrong...
A complet parabola will reflect all the light from one focus to the other. We know this and that has been the hype about building ellipsoidal reflectors. Howevers, the light does not just all head over that way....a lot of light needs to bounce off the reflector on the destination side...since we are only using the source half of the ellipse, and ideally placing just an LCD there, we be losing a good chunck of light This is beacuse the light that has not been reflected off our reflector (the light that starts off directed away from the reflector) is expected to bounce of the other side of the ellipse in order to properly reach the focus....This is why I am going to use a Fresnel still even though I am using an ellipsoidal reflector. If I throw my fresnels right at the end of the reflector I will get almost ALL of the light that is being emitted from my bulb (assuming I have a highly reflective surface). The fresnel can then focus the light throught the LCD and down to my projection lens.
The only reason I was thinking of a parabolic reflector is so I can send the light out in parallel and hope it gathers more light...I could also possible remove the first fresnel if I had parallel rays soming in.

I hope this makes sense...please let me know what you think...I will try to draw some pictures to show what I mean.

Later,
Dave

[DPW666]

superdave,
what lens are you using for projection? Also, have you tried to cover the light source so everyting is light tight expect for the lcd? Like a box over the light so the only light that comes out is from the lcd.

[SuperDave]

DPW666...right now I am just using the lens I took from my ELMO OHP. Its nothing special but it works. I am using the fresnels from it too...so I have a section of my screen cropped out.

Also...yes I have enclosed it so barely any light escapes but I still am not getting much light output through the fresnels...You have to remember that I just bought a metal bowl and hoped that would help (unfortunaletly it didnt and now I have a bowl with a hole).
You can look at my webpage and see pictures of my funky-box-case.

http://www.csun.edu/~hbpsy028/projec...p/Image025.jpg

[SuperDave]

OK...the 3 pictures below detail why I think the fresnels are still needed.
the first drawing shows the light path of an entire elliptical reflector...

the second show how we lost a good portion of light if we only use a reflector and LCD...it has been suggested a number of times that fresnels will not be neede. Although the are not necessary we will get more use of our light if we use them.

the third show how the use of fresnels will make use of almost all light produced from our bulb.